Semiconductor device with elongated interconnecting member and fabrication method thereof

ABSTRACT

In a semiconductor device with multiple wiring layers, to connect a conductive line in a lower wiring layer to a conductive line in an upper wiring layer, two conductive members are formed in the space between the upper and lower conductive layers, one conductive member in contact with each conductive line. The two conductive members meet in the space between the two conductive layers to form an electrical path between the two conductive lines. One or both of the conductive members may have a rectangular bar shape extending lengthwise along the conductive line with which it makes contact. The conductive members can have a reduced height and enlarged area that enables interconnections to be formed with greater stability and reliability than by conventional methods.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device havingmultilayer wiring, and more particularly to a method of forminginterconnections between an upper wiring layer and a lower wiring layer.

[0003] 2. Description of the Related Art

[0004]FIG. 14 shows a partial sectional view of a conventionalsemiconductor device having a lower conductive layer or wiring layerincluding a first conductive line or wire 61, an inter-layer dielectricfilm 62 with a through hole 63, and an upper conductive layer or wiringlayer including a second conductive line or wire 64 that is connected tothe lower-layer wire 61 by a metal plug filling the through hole 63. Thethrough hole 63 has a depth d, radius r, and diameter 2 r.

[0005] The multilayer wiring structure shown in FIG. 14 is fabricated asfollows. First, a layer of metal is deposited on the entire surface ofthe device and patterned by photolithography and etching to form alower-layer pattern of conductive lines 61. Next, the inter-layerdielectric film 62 is deposited on the entire surface and planarized bychemical-mechanical polishing (CMP). The inter-layer dielectric film 62comprises a dielectric material such as silicate glass. The inter-layerdielectric film 62 is then etched to create through holes 63 atpositions where the lower-layer conductive lines 61 will be connected toupper-layer conductive lines 64, and the through holes 62 are filledwith metal. Another layer of metal is then deposited on the entiresurface and patterned by photolithography and etching to create theupper-layer conductive lines 64.

[0006] As semiconductor device geometries have shrunk, so has thediameter (2 r) of the through holes, and their aspect ratio (d/πr²) hasincreased. As a result, it has become difficult to assure the stableformation of a resist pattern for the small-diameter through holes inthe photolithographic process, and to assure that the through holes willbe etched to a constant depth during the etching process. The result isunreliable connections between the different wiring layers of asemiconductor device with multilayer wiring. The problem of theformation of a reliable connection structure for multilayer wiring hashindered progress toward devices with still smaller geometries.

[0007] A further problem is that if the depth d of the through holes isreduced as their diameter is reduced, the reduced spacing between wiringlayers increases the parasitic capacitance of the wiring. The limitingdimensions for the stable formation of interconnections betweendifferent wiring layers in conventional semiconductor devices have been,for example, a through-hole diameter of one-fifth of a micrometer (2r=0.2 μm) and a through-hole depth of one-half of a micrometer (d=0.5μm).

SUMMARY OF THE INVENTION

[0008] An object of the present invention is accordingly to provide asemiconductor device with a multilayer wiring interconnection structurethat permits smaller device geometries.

[0009] Another object of the invention is to provide a fabricationmethod for such a semiconductor device.

[0010] The invented semiconductor device includes a first conductivelayer and a second conductive layer. To connect a conductive line orpattern in the first conductive layer to a conductive line or pattern inthe second conductive layer, a pair of conductive members or conductorsare formed between the two conductive layers, both conductive membershaving heights less than the separation between the conductive layers.One conductive member makes contact with or is unitary with theconductive line or pattern in the lower conductive layer; the otherconductive member makes contact with or is unitary with the conductiveline or pattern in the upper conductive layer. The two conductivemembers extend for different distances in at least one directionparallel to the conductive layers. The two conductive members makemutual contact, thereby establishing an electrical path between the twoconductive lines. One conductive member may be slotted to receive theother conductive member.

[0011] In one fabrication method for the invented semiconductor device,after a lower conductive layer is formed and patterned, a firstdielectric film is deposited, covering the lower conductive layer. Thefirst dielectric film is patterned to form a first hole extending to aconductive line or pattern in the lower conductive layer, and the firsthole is filled with a conductive material to form a first conductivemember or conductor. A second dielectric film is then deposited on thefirst dielectric film, and patterned to form a second hole extending tothe first conductive member. The second hole is filled with a conductivematerial to form a second conductive member or conductor making contactwith the first conductive member or conductor, and an upper conductivelayer is formed on the second dielectric film. The upper conductivelayer includes a conductive line or pattern making contact with thesecond conductive member.

[0012] In this method, the second conductive member and the upperconductive layer may be formed in a single step, by depositing a layerof conductive material that covers the second dielectric film and fillsthe second hole, then patterning this layer of conductive material toform the upper conductive layer. The second conductive member, disposedin the second hole, is unitary with a conductive line or pattern in theupper conductive layer.

[0013] Alternatively, the upper conductive layer may be formed bydepositing a third dielectric film, patterning the third dielectric filmto form trenches, and filling the trenches with a conductive material.The conductive material may be copper.

[0014] Similarly, the lower conductive layer may be formed by depositinga dielectric film, patterning the dielectric film to form trenches, andfilling the trenches with a conductive material such as copper.

[0015] In another fabrication method for the invented semiconductordevice, the lower conductive layer is formed in a two-step process thatalso forms the first conductive member or conductor. Specifically, aconductive film is patterned to form a conductive pattern. A coating ofphotoresist is applied, covering the conductive pattern, and the coatingis patterned by photolithography to leave a mask that masks part of theconductive pattern. The exposed part of the conductive pattern is thenetched to reduce its height. The part of the conductive pattern that isnot etched because it is below the level at which etching is stoppedbecomes the lower conductive layer. A masked part of the conductivepattern remaining above this level becomes the first conductive member,which is unitary with the lower conductive layer. The second conductivemember and the upper conductive layer are then formed substantially asdescribed above, by depositing a dielectric film, forming a hole in thedielectric film extending to the first conductive member, filling thehole with a conductive material, and forming a conductive layer on thedielectric film.

[0016] Either fabrication method may by adapted to form a slot in thefirst conductive member to receive the second conductive member. Forexample, after the hole for the second conductive member has beenformed, the first conductive member may be etched to create such a slot.

[0017] Needless to say, either fabrication method may be adapted to forma plurality of first conductive members and a plurality of secondconductive members.

[0018] The invention enables the wiring dimensions of a semiconductordevice to be reduced by reducing the widths of the conductive memberswithout requiring an equal reduction of the lengths of the conductivemembers. Specifically, a conductive member having an elongated shapesuch as a rectangular bar shape can be made narrow enough to permit veryfine, closely-spaced conductive lines, while still being long enough toensure that the conductive member is reliably formed. Furthermore, if anelectrical path between two conductive layers is created by a conductorhaving the form of an elongated bar meeting a conductor having the formof a plug, the hole for the plug-shaped conductor can be shallow enoughto ensure reliable formation of the plug-shaped conductor, while theadditional height of the bar-shaped conductor permits sufficientseparation between the two conductive layers to avoid problems caused byparasitic capacitance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the attached drawings:

[0020]FIG. 1A is a partial plan view of a semiconductor deviceillustrating a first embodiment of the invention;

[0021]FIG. 1B is a sectional view along line x-x′ in FIG. 1A;

[0022]FIG. 1C is a sectional view along line y-y′ in FIG. 1A;

[0023]FIG. 2A is another partial plan view of a semiconductor deviceillustrating the first embodiment;

[0024]FIG. 2B is a sectional view along line x-x′ in FIG. 2A;

[0025]FIG. 2C is a sectional view along line y-y′ in FIG. 2A;

[0026]FIG. 3A is another partial plan view of a semiconductor deviceillustrating the first embodiment;

[0027]FIG. 3B is a sectional view along line x-x′ in FIG. 3A;

[0028]FIG. 3C is a sectional view along line y-y′ in FIG. 3A;

[0029]FIG. 4A is another partial plan view of a semiconductor deviceillustrating the first embodiment;

[0030]FIG. 4B is a sectional view along line x-x′ in FIG. 4A;

[0031]FIG. 4C is a sectional view along line y-y′ in FIG. 4A;

[0032]FIG. 5 is a partial plan view of a semiconductor deviceillustrating the first embodiment, indicating different possible lengthsof the rectangular metal bars;

[0033]FIGS. 6A, 6B, and 6C illustrate steps in a first fabricationmethod for the first embodiment;

[0034]FIGS. 7A, 7B, and 7C illustrate steps in a second fabricationmethod for the first embodiment;

[0035]FIGS. 8A, 8B, 8C, 8D, and 8E illustrate steps in a thirdfabrication method for the first embodiment;

[0036]FIGS. 9A, 9B, and 9C illustrate steps in a fourth fabricationmethod for the first embodiment;

[0037]FIG. 10A is a partial plan view of a semiconductor deviceillustrating a second embodiment of the invention;

[0038]FIG. 10B is a sectional view along.line x-x′ in FIG. 10A;

[0039]FIG. 10C is a sectional view along line y-y′ in FIG. 10A;

[0040]FIG. 11A is another partial plan view of the semiconductor deviceillustrating the second embodiment;

[0041]FIG. 11B is a sectional view along line x-x′ in FIG. 11A;

[0042]FIG. 11C is a sectional view along line y-y′ in FIG. 11A;

[0043]FIG. 12A is a partial plan view of a semiconductor deviceillustrating a third embodiment of the invention;

[0044]FIG. 12B is a sectional view along line x-x′ in FIG. 12A;

[0045]FIG. 12C is a sectional view along line y-y′ in FIG. 12A;

[0046]FIG. 13A is a partial plan view of a semiconductor deviceillustrating a fourth embodiment of the invention;

[0047]FIG. 13B is a sectional view along line x-x′ in FIG. 13A;

[0048]FIG. 13C is a sectional view along line y-y′ in FIG. 13A; and

[0049]FIG. 14 is a sectional view showing the structure of aconventional semiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

[0050] Embodiments of the invention will now be described with referenceto the attached drawings, in which like elements are indicated by likereference characters.

[0051] In the following description and the appended claims, the termsconductive line, conductive pattern, and wire will be used withsubstantially the same meaning; dielectric films will also be referredto as insulating films; and the terms conductive member and conductorwill be treated as synonyms.

[0052] First Embodiment

[0053] The structure of a semiconductor device according to the firstembodiment is illustrated in FIGS. 1A to 4C. As shown in these drawings,the semiconductor device includes a first conductive line or firstconductive pattern 1 in a lower conductive layer, a first conductivemember or first conductor in the form of a rectangular metal bar 2, aninter-layer dielectric film 3, a second conductive member or secondconductor in the form of a rectangular metal bar 4, and a secondconductive line or second conductive pattern 5 in an upper conductivelayer. Both conductive lines (or patterns) 1, 5 have a line width LW,rectangular metal bar 2 has height H1, and rectangular metal bar 4 hasheight H2. The separation d between the upper conductive layer and thelower conductive layer is the sum of heights H1 and H2.

[0054] In each drawing, rectangular metal bar 2 is aligned above and incontact with lower-layer conductive line 1, while rectangular metal bar4 is aligned below and in contact with upper-layer conductive line 5. InFIG. 1A, the conductive lines 1, 5 are both straight, and cross atsubstantially a right angle; rectangular metal bar 2 is a straight barwith length L1 and width W1, while rectangular metal bar 4 is a straightbar with length L2 and width W2. Both bars are centered at the point atwhich conductive line 1 crosses conductive line 5. As shown in FIGS. 1Band 1C, the rectangular metal bars 2, 4 are in mutual contact at thispoint. In FIGS. 2A to 4C, lower-layer conductive line 1 bends atsubstantially a right angle and is connected to upper-layer conductiveline 5 at or near the bend. In FIGS. 2A to 3C, rectangular metal bar 2has a modified rectangular shape that follows the bend.

[0055] In the semiconductor device according to the first embodiment,rectangular metal bar 2 is aligned above the lower-layer conductive line1, and extends for part of the length of the lower-layer conductive line1, while rectangular metal bar 4 is aligned below the upper-layerconductive line 5, and extends for part of the length of the upper-layerconductive line 5. Rectangular metal bar 2 is formed in contact with oris unitary with the lower-layer conductive line 1; rectangular metal bar4 is formed in contact with or is unitary with the upper-layerconductive line 5. Rectangular metal bar 2 makes contact withrectangular metal bar 4, establishing an electrical path between thelower-layer conductive line 1 and the upper-layer conductive line 5.

[0056] In the first embodiment, the sum of the height H1 of rectangularmetal bar 2 and the height H2 of rectangular metal bar 4 is equal to theseparation d between the lower-layer conductive line 1 and theupper-layer conductive line 5 (d=H1+H2), so neither rectangular metalbar is as high as the separation d (d>H1 and d>H2). The width W1 ofrectangular metal bar 2 is equal to the line width LW of conductive line1, and the width W2 of rectangular metal bar 4 is equal to the linewidth LW of conductive line 5 (W1=W2=LW). The length L1 of rectangularmetal bar 2 is set to a value exceeding the width W1 of the lower-layerconductive line 1, while the length L2 of rectangular metal bar 4 is setto a value exceeding the width W2 of the upper-layer conductive line 5(L1>W1=LW, and L2>W2=LW).

[0057] A semiconductor device according to the first embodiment isdesigned on the basis of given multilayer wiring pattern rules. As anexample of such rules, if the line width LW is 0.2 μm and the separationd between the lower-layer conductive line 1 and the upper-layerconductive line 5 is 0.5 μm, then the height H1 of rectangular metal bar2 and the height H2 of rectangular metal bar 4 are both 0.25 μm, thewidth W1 of rectangular metal bar 2 and the width W2 of rectangularmetal bar 4 are both 0.2 μm, and the length L1 of rectangular metal bar2 and the length L2 of rectangular metal bar 4 are both 0.4 μm. Thelengths L1 and L2 are unconstrained, provided that L1 and L2 are bothequal to or greater than the line width LW. For comparison, if theconventional semiconductor device in FIG. 14 is designed on the basis ofthe same rules, the diameter 2 r of the through hole 63 is 0.2 μm, whichis the same as the wiring line width, and the depth of the through hole63 is 0.5 μm, being equal to the separation d between the lower-layerconductive line 1 and the upper-layer conductive line 5.

[0058] Thus if a semiconductor device according to the first embodimentis designed according to the same pattern rules as a conventionalsemiconductor device, the heights H1 and H2 of the rectangular metalbars 2, 4 are both less than the conventional through-hole depth, theirwidths W1 and W2 are both the same as the conventional through-holediameter 2 r, and their lengths L1 and L2 exceed the conventionalthrough-hole diameter 2 r. The lengths of the rectangular metal bars 2,4 also exceed the conventional through-hole diameter 2 r in the wiringpatterns with right-angle bends illustrated in FIGS. 2A to 4C.Furthermore, the pattern area (W1×L1) of rectangular metal bar 2 and thepattern area (W2×L2) of rectangular metal bar 4 exceed the pattern area(πr²) of the conventional through hole. The aspect ratio (H1/(W1×L1) ofrectangular metal bar 2 and the aspect ratio (H2/(W2×L2) of rectangularmetal bar 4 are thus less than the aspect ratio (d/·r²) of theconventional through hole, and the area (W1×W2=LW²) of contact betweenthe rectangular metal bars 2, 4 exceeds the area of contact of theconventional through hole with the upper and lower conductive layers.

[0059] The pattern areas of the rectangular metal bars 2, 4 can thus beincreased while their aspect ratios are decreased, as compared with aconventional through hole. Consequently, the process of formingrectangular holes that will be filled with metal to create therectangular metal bars 2, 4 is more stable than the process of formingconventional through holes. Alternatively, the lower rectangular metalbar 2 can be formed by photolithography and etching of the lower metalconductive layer, and this process is also more stable than theformation of conventional through holes. Interconnections betweendifferent conductive layers can therefore be formed with greaterstability than in a conventional semiconductor device, and thereliability of the interconnections can be improved.

[0060] Furthermore, since the lengths L1, L2 of the rectangular metalbars 2, 4 exceed the conventional through-hole diameter 2 r, in aphotolithographic process for forming rectangular metal bar 4 or itsrectangular hole, the alignment tolerance with respect to rectangularmetal bar 2 can be greater than the alignment tolerance with respect tothe lower conductive layer in the photolithographic process for formingconventional through holes. A larger alignment tolerance can also beallowed in the photolithographic process for forming the upperconductive layer than can be allowed when conventional through holes areemployed. For this reason as well, different conductive layers can beinterconnected by a more stable process than in a conventionalsemiconductor device, and the reliability of the interconnections can beimproved.

[0061] Since the area of contact between the rectangular metal bars 2, 4is also increased, as compared with the contact areas in a conventionalsemiconductor device, current is distributed over a larger area, and thecurrent density at the interface between the rectangular metal bars 2, 4is lower than the current density at the interfaces of a conventionalthrough hole. This further improves the reliability of theinterconnections.

[0062] The interconnecting structure in FIGS. 2A to 2C, in which theupper-layer conductive line 5 and rectangular metal bar 4 terminateabove the bend in the lower-layer conductive line 1, provides anincreased alignment tolerance for rectangular metal bar 4 in the x′ andy directions, but not in the x and y′ directions. This leads toconsideration of the interconnecting structures illustrated in FIGS. 3Ato 4C. In FIGS. 3A to 3C, the ends of the upper-layer conductive line 5and rectangular metal bar 4 are extended in the y direction, increasingthe alignment tolerance in the y direction, and also increasing thecontact area between the rectangular metal bars 2, 4. In FIGS. 4A to 4C,the ends of the upper-layer conductive line 5 and rectangular metal bar4 are extended in the y direction, and the upper-layer conductive line 5and rectangular metal bar 4 are shifted in the x′ direction, increasingthe alignment tolerance in the x and y′ directions.

[0063] In the semiconductor device of the first embodiment, since thelower-layer conductive line 1 and upper-layer conductive line 5 areinterconnected through a pair of elongated metal bars 2, 4 with reducedheights and lowered aspect ratios, for given design rules, a more stableinterconnection is formed than in the conventional structure. Moreover,the interconnection formation process remains stable even when thedesign rules are scaled down and the widths of the conductive lines andthe rectangular metal bars are reduced. Interconnection reliability cantherefore be improved, and semiconductor devices with smaller geometriescan be fabricated.

[0064] Since the lengths L1, L2 of the rectangular metal bars 2, 4 areunconstrained, they can be optimized according to such factors asparasitic capacitance between the upper and lower conductive layers,photolithographic alignment tolerances, and multilayer wiring designrules.

[0065] When a plurality of upper-layer and lower-layer conductive lines1, 5 are laid out, in principle, the lengths L1, L2 of the rectangularmetal bars 2, 4 are not constrained by the conductive line spacing inthe upper and lower layers. However, in the special case in which oneinterconnection between the upper and lower conductive layers isdisposed near another interconnection between different conductive linesin the upper and lower conductive layers, it may be necessary torestrict the lengths L1 and L2 to avoid unwanted contact between the twointerconnections, as will be described below.

[0066] Although increasing the lengths L1, L2 of the rectangular metalbars 2, 4 increases the photolithographic alignment tolerances, as thelengths L1, L2 increase, the rectangular metal bars 2, 4 may approachcloser to conductive lines to which they are not connected in the upperand lower layers, so the parasitic capacitance between the rectangularmetal bars and the upper and lower conductive layers increases. For thisreason, the lengths L1, L2 of the rectangular metal bars 2, 4 should beselected to obtain an optimum balance between more lenientphotolithographic alignment tolerances and increased parasiticcapacitance between the upper and lower conductive layers.

[0067] The lengths of the rectangular metal bars are further explainedin FIG. 5. Reference characters 1A and 1B denote a pair of mutuallyadjacent conductive lines in the lower conductive layer; 5A and 5Bdenote a pair of mutually adjacent conductive lines in the upperconductive layer; 2A and 2B denote first rectangular metal bars formedon conductive lines 1A and 1B, respectively; 4A and 4B denote secondrectangular metal bars formed below conductive lines 5A and 5B,respectively; L1a, L1b, and L1c denote three possible lengths ofrectangular metal bar 4B; L2a, L2b, and L2c denote three possiblelengths of rectangular metal bar 2A; LW denotes the width of conductivelines 1A, 1B, 5A, and 5B; and P denotes the pitch or spacing ofconductive lines 1A and 1B, and of conductive lines 5A and 5B. The widthLW of the conductive lines in both the upper and lower conductive layersis 0.2 μm, while the upper and lower conductive line pitch P is 0.4 μm.The lengths L2a and L1a of rectangular metal bars 2A and 4B are bothgreater than 0.5 P (=LW) and both less than 1.5 P. For the samerectangular metal bars 2A, 4B, lengths L2b and L1b are both greater than1.5 P, and lengths L2c and L1c are both strictly between 1.5 P and 2.5P. Lower-layer conductive line 1A and upper-layer conductive line 5A areinterconnected where they cross, by contact between rectangular metalbars 2A and 4A; similarly, lower-layer conductive line 1B andupper-layer conductive line 5B are interconnected where they cross, bycontact between rectangular metal bars 2B and 4B.

[0068] In FIG. 5, if the length of rectangular metal bar 2A is set toL2b, extending to a position below upper-layer conductive line 5B, andif the length of rectangular metal bar 4B is set to L1b, extending to aposition above lower-layer conductive line 1A, then rectangular metalbar 2A will meet rectangular metal bar 4B at the crossover betweenlower-layer conductive line 1A and upper-layer conductive line 5B. Thisunwanted contact can be avoided by restricting rectangular metal bar 2Ato length L2a, so that it does not extend below upper-layer conductiveline 5B, and restricting rectangular metal bar 4B to length L1a, so thatit does not extend above lower-layer conductive line 1A. Lengths L2a andL1a may both be set equal to 0.4 μm (=P), for example. Alternatively,the length of one of the two rectangular metal bars 2A, 4B can berestricted to L2a or L1a, and the length of the other one of these tworectangular metal bars 2A, 4B can be left as L2b or L1b. Similarconsiderations hold for rectangular metal bars 4A and 2B.

[0069] To generalize from the special case shown in FIG. 5, when aninterconnection between a first pair of upper- and lower-layerconductive lines is laid out near an unrelated interconnection between asecond pair of upper- and lower-layer conductive lines, to which thefirst pair of upper- and lower-layer conductive lines should not beconnected, if the rectangular metal bars are made so long as to bridgethe distance between the first and second pairs of conductive lines inboth conductive layers (e.g., lengths L1b and L2b), unintendedelectrical connections may be created. To avoid this, the rectangularmetal bars of one conductive layer or the other should be limited to alength (such as L1a or L2a) that keeps them from reaching the positionsof conductive lines in the opposite conductive layer to which they neednot be connected.

[0070] If lower-layer conductive line 1B in FIG. 5 is not connected toupper-layer conductive line 5B, then rectangular metal bars 2B and 4Bare not present, so the lengths of rectangular metal bars 2A and 4A arenot subject to the above constraints. Rectangular metal bar 2A can thenbe set to either length L2a or L2b, and rectangular metal bar 4A toeither length L1a or L1b, regardless of the conductive line pitch P inthe upper and lower conductive layers and the layout of thesemiconductor device.

[0071] The longer the rectangular metal bars 2A, 2B, 4A, 4B are in FIG.5, the greater the photolithographic alignment tolerances become, butthe spacing between rectangular metal bar 2A and upper-layer conductiveline 5B, between rectangular metal bar 2B and upper-layer conductiveline 5A, between rectangular metal bar 4A and lower-layer conductiveline 1B, and between rectangular metal bar 4B and lower-layer conductiveline 1A is reduced. Consequently, the parasitic capacitance betweenlower-layer conductive line 1A and upper-layer conductive line 5B, andbetween lower-layer conductive line 1B and upper-layer conductive line5A, also increases. Thus, even when the lengths of the rectangular metalbars 2A, 2B, 4A, 4B are set within the limits of L2a and L1a, if largealignment tolerances are not required and parasitic capacitance needs tobe reduced, the rectangular metal bars 2A, 2B, 4A, 4B should be maderelatively short. Similarly, when there is not so much need to reduceparasitic capacitance and larger alignment tolerances are desired, therectangular metal bars should be made relatively long.

[0072] If lower-layer conductive line 1A is to be connected toupper-layer conductive line 5B in FIG. 5, rectangular metal bars 2A and4B can be brought into contact by setting their lengths to L2c and L1c.Length L2c is obtained by extending length L2a in the direction ofupper-layer conductive line 5B, so that rectangular metal bar 2A passescompletely under upper-layer conductive line 5B. Length L1c is obtainedby extending length L1a in the direction of lower-layer conductive line1A so that rectangular metal bar 4B passes completely over lower-layerconductive line 1A. Lengths L1c and L2c are equal, both being 0.8 μm,for example.

[0073] A first method of fabricating a semiconductor device according tothe first embodiment is illustrated in FIGS. 6A to 6C, which show theformation of the wiring structure in FIGS. 2A to 2C.

[0074] Referring to FIG. 6A, films of a barrier metal (such as titanium)and aluminum are deposited on the surface of a dielectric film thatforms a substrate for the lower conductive layer, and the resultingmetal layer is patterned by photolithography and etching to form thelower conductive layer, including conductive line 1.

[0075] Next, a first inter-layer dielectric film 3 a comprising amaterial such as silicate glass is deposited on the entire surface andplanarized by CMP. A rectangular hole 6 is then formed in the firstinter-layer dielectric film 3 a by photolithography and etching. Thephotoresist film used to create an etching mask for the rectangular hole6 has a thickness of substantially eight thousand to nine thousandangstroms (8000-9000 Å). The rectangular hole 6 is formed over andaligned with part of lower-layer conductive line 1, and exposes thesurface of this part of lower-layer conductive line 1.

[0076] Next, films of a barrier metal (such as titanium) and tungstenare deposited on the entire surface, filling in the rectangular hole 6.The resulting metal layer is planarized by CMP, removing the metaldeposited outside the rectangular hole 6 and leaving rectangular metalbar 2.

[0077] Referring to FIG. 6B, a second inter-layer dielectric film 3 bcomprising a material such as silicate glass is deposited on the entiresurface, and a rectangular hole 7 is formed in this film 3 b byphotolithography and etching. The rectangular hole 7 is aligned with theprospective location of part of an upper-layer conductive line 5, andexposes part of the surface of rectangular metal bar 2. The first andsecond inter-layer dielectric films 3 a, 3 b constitute the inter-layerdielectric film 3 mentioned above.

[0078] Next, films of a barrier metal (such as titanium) and tungstenare deposited on the entire surface, filling in the rectangular hole 7.The resulting metal layer is planarized by CMP, removing the metaloutside the rectangular hole 7 and leaving rectangular metal bar 4.

[0079] Referring to FIG. 6C, films of a barrier metal (such as titanium)and aluminum are deposited on the entire surface, and the resultingmetal layer is patterned by photolithography and etching to form theupper conductive layer, including conductive line 5. This completes thewiring structure according to the first embodiment.

[0080] In this first fabrication method, as the surface areas of therectangular holes 6, 7 exceed those of a conventional through hole, andthe rectangular holes 6, 7 are shallower than a conventional throughhole, making the aspect ratios of the rectangular holes 6, 7 smallerthan the aspect ratio of the through hole, for the same design rules,the rectangular holes 6, 7 can be formed by photolithography and etchingwith greater stability than can a conventional through hole. Since therectangular holes 6, 7 are longer than the diameter of the conventionalthrough hole, they also have less stringent photolithographic alignmenttolerances. Furthermore, the greater surface areas of the rectangularmetal bars 2, 4 produce a lower current density at the interface betweenthem, as compared with a conventional through hole. For these reasons,the process of forming interconnections between different conductivelayers becomes more stable, the reliability of the interconnections isimproved, and smaller device geometries become feasible.

[0081]FIGS. 7A, 7B, and 7C illustrate a second method of fabricating asemiconductor device with the wiring structure in FIGS. 2A to 2C.

[0082] First, referring to FIG. 7A, films of a barrier metal (such astitanium) and aluminum are deposited on the entire surface ofa-dielectric film that-serves as a wiring substrate, forming aconductive film. The conductive film is patterned to form a conductivepattern, one part of which is a conductive line pattern that will becomelower-layer conductive line 1; then a coating of photoresist is appliedand patterned by photolithography to form a mask that partly covers theconductive pattern. The exposed parts of the conductive pattern areetched to reduce their height to the desired height of the lowerconductive layer, e.g., the height of conductive line 1. The maskedparts of the conductive pattern that are left intact above this heightform rectangular metal bars such as the rectangular metal bar 2 in FIG.7A.

[0083] Thus according to the second fabrication method, the conductivefilm formed on the substrate is patterned by photolithography andetching twice to form the lower conductive layer and its attachedrectangular metal bars. If the two photolithography and etchingprocesses are carried out as described above, rectangular metal bar 2 isself-aligned with lower-layer conductive line 1. It is also possible,however, to form the lower-layer conductive line 1 and rectangular metalbar 2 in the opposite order from that described above. That is,rectangular metal bar 2 can be patterned by the first photolithographyand etching process, and lower-layer conductive line 1 by the secondphotolithography and process.

[0084] Next, referring to FIG. 7B, an inter-layer dielectric film 3 isdeposited on the entire surface and planarized by CMP, and a rectangularhole 7 is formed in this film 3 by photolithography and etching. Therectangular hole 7 is aligned with the prospective location of part ofan upper-layer conductive line 5, and exposes part of the surface ofrectangular metal bar 2.

[0085] Next, referring to FIG. 7C, films of a barrier metal (such astitanium) and aluminum are deposited on the entire surface to form ametal layer that fills the rectangular hole 7. The metal layer is thenpatterned by photolithography and etching to form rectangular metal bar4 and the upper-layer conductive line 5 simultaneously, completing thewiring structure according to the first embodiment.

[0086] Like the first fabrication method, the second fabrication methodenables smaller device geometries to be achieved. In addition,rectangular metal bar 2 can be self-aligned with lower-layer conductiveline 1, further enhancing the stability of the interconnection formationprocess, as compared with the formation of conventional through holeswith the same design rules.

[0087] In the second fabrication method, the lower-layer conductive line1 is unitary with rectangular metal bar 2, being formed from the samemetal layer, and the upper-layer conductive line 5 is unitary withrectangular metal bar 4, both being formed from another metal layer, soconnection faults such as high contact resistance and open circuits areless likely to occur than in the first fabrication method.

[0088] The second fabrication method is also simpler than the firstfabrication method in that the lower-layer conductive line 1 andrectangular metal bar 2 are formed by two photolithography and etchingprocesses applied to the same metal layer, and rectangular metal bar 4and upper-layer conductive line 5 are formed by a singlephotolithography and etching process performed on a single metal layer.

[0089] The above two fabrication methods can be combined. Thelower-layer conductive line 1 and rectangular metal bar 2 can be formedby the first fabrication method, while rectangular metal bar 4 and theupper-layer conductive line 5 are formed by the second fabricationmethod. Alternatively, the lower-layer conductive line 1 and rectangularmetal bar 2 can be formed by the second fabrication method, whilerectangular metal bar 4 and the upper-layer conductive line 5 are formedby the first fabrication method.

[0090]FIGS. 8A to 8 e illustrate a third method of fabricating asemiconductor device with the wiring structure in FIGS. 2A to 2C.

[0091] The third fabrication method employs a damascene process. In thisprocess, trenches are formed in a dielectric film, then filled withmetal to form conductive lines. The damascene process permits theformation of conductive lines from a low-resistance metal material suchas copper.

[0092] Referring to FIG. 8A, a first inter-layer dielectric film 3 acomprising a material such as silicate glass is deposited on the entiresurface of a dielectric film which forms a substrate for the lowerconductive layer. Then, a trench 8 is formed in each part of the firstinter-layer dielectric film 3 a in which a conductive line in the lowerconductive layer will be formed, by photolithography and etching.

[0093] Next, films of a barrier metal (such as titanium) and copper aredeposited on the entire surface, forming a metal layer that fills thetrenches. The surface is then planarized by CMP, removing the metallayer from regions outside the trenches, leaving a lower-layerconductive line 1 in trench 8.

[0094] Next, referring to FIG. 8B, a second inter-layer dielectric film3 b comprising a material such as silicate glass is deposited on theentire surface, and a rectangular hole 6 is formed in the secondinter-layer dielectric film 3 b by photolithography and etching. Therectangular hole 6 is aligned with part of lower-layer conductive line1, and exposes the surface of that part of lower-layer conductive line1.

[0095] Next, films of a barrier metal (such as titanium) and tungstenare deposited on the entire surface to form a metal layer that fills therectangular hole 6. The surface is then planarized by CMP, removing thismetal layer from regions outside the rectangular hole 6 to form arectangular metal bar 2.

[0096] Next, referring to FIG. 8C, an inter-layer dielectric film 3 ccomprising a material such as silicate glass is deposited on the entiresurface, and a rectangular hole 7 is formed in the inter-layerdielectric film 3 c by photolithography and etching. The rectangularhole 7 is aligned with the prospective location of part of anupper-layer conductive line 5, and exposes part of the surface ofrectangular metal bar 2.

[0097] Next, films of a barrier metal (such as titanium) and tungstenare deposited on the entire surface, forming a metal layer that fillsthe rectangular hole 7. The surface is then planarized by CMP, removingthis metal layer from regions outside the rectangular hole 7 to form arectangular metal bar 4.

[0098] Next, referring to FIG. 8D, an inter-layer dielectric film 3 dcomprising a material such as silicate glass is deposited on the entiresurface, and a trench 9 is formed in each part of the 3 d in which aconductive line in the upper conductive layer will be formed, byphotolithography and etching. The trench 9 exposes part of the surfaceof rectangular metal bar 4.

[0099] Next, referring to FIG. 8E, films of a barrier metal (such astitanium) and copper are deposited on the entire surface to form a metallayer covering the trench 9. The surface is then planarized by CMP,removing this metal layer from regions outside the trench 9 to form theupper-layer conductive line 5 in the trench 9, thus completing thewiring structure according to the first embodiment.

[0100] Like the first fabrication method, the third fabrication methodenables smaller device geometries to be achieved. By forming theconductive lines 1, 5 by the damascene process, the third fabricationmethod also enables low-resistance conductive lines to be formed with ahigh density.

[0101]FIGS. 9A to 9C illustrate a fourth method of fabricating asemiconductor device with the wiring structure in FIGS. 2A to 2C.

[0102] The fourth fabrication method employs a dual damascene process.In this process, a conductive line and a rectangular metal bar areformed in a single dielectric film. A trench for the conductive line anda rectangular hole for the rectangular metal bar are formed; then boththe trench and the rectangular hole are filled with a metal such ascopper, forming the conductive line and the rectangular metal barsimultaneously.

[0103] First, referring to FIG. 9A, a first inter-layer dielectric film3 a comprising a material such as silicate glass is deposited on theentire surface of a dielectric film which forms the substrate for thelower conductive layer. A trench 8 is formed in each part of the firstinterlayer dielectric film 3 a in which a conductive line in the lowerconductive layer will be formed, by photolithography and etching.

[0104] Next, films of a barrier metal (such as titanium) and copper aredeposited on the entire surface to form a metal layer filling the trench8. The surface is then planarized by CMP, removing the metal layer fromregions outside the trench 8 to form a lower-layer conductive line 1 inthe trench 8.

[0105] Next, a second inter-layer dielectric film 3 b comprising amaterial such as silicate glass is deposited on the entire surface, anda rectangular hole 6 is formed in the second inter-layer dielectric film3 b by photolithography and etching. The rectangular hole 6 is alignedwith part of the lower-layer conductive line 1, and exposes the surfaceof that part of the lower-layer conductive line 1.

[0106] Next, films of a barrier metal (such as titanium) and copper aredeposited on the entire surface to form a metal layer filling therectangular hole 6. The surface is then planarized by CMP, removing themetal layer from regions outside the rectangular hole 6 to form arectangular metal bar 2.

[0107] Next, referring to FIG. 9B, an inter-layer dielectric film 3 ccomprising a material such silicate glass is deposited on the entiresurface. Then photolithography and etching are performed twice to form atrench 9 and a rectangular hole 7 in the inter-layer dielectric film 3c. A trench 9 is formed in each part of the inter-layer dielectric film3 c in which a conductive line in the upper conductive, layer will beformed. The rectangular hole 7 is aligned below the trench 9, extendsfor part of the length of the trench 9, and exposes part of the surfaceof rectangular metal bar 2. The trench 9 and the rectangular hole 7 maybe formed in either order: the trench 9 may be formed by the firstphotolithography and etching process and the rectangular hole 7 by thesecond photolithography and etching process, or this order may bereversed.

[0108] Next, referring to FIG. 9C, films of a barrier metal (such astitanium) and copper are deposited on the entire surface to form a metallayer that fills the rectangular hole 7 and trench 9. The surface isthen planarized by CMP, removing the metal layer from regions outsidethe rectangular hole 7 and trench 9 to form a rectangular metal bar 4and upper-layer conductive line 5 simultaneously. This completes theformation of a wiring structure according to the first embodiment.

[0109] Like the first fabrication method, the fourth fabrication methodenables smaller device geometries to be achieved. By forming thelower-layer conductive line 1 and upper-layer conductive line 5 by thedamascene process, the fourth fabrication method also enableslow-resistance, high-density conductive lines to be formed, as in thethird fabrication method. Use of the dual damascene process furtherenables rectangular metal bar 4 and upper-layer conductive line 5 to beformed from a single metal layer, so that they are unitary with eachother, and only one metal deposition process is necessary. The unitarystructure reduces the likelihood of connection faults such as highcontact resistance or an open circuit between rectangular metal bar 4and the upper-layer conductive line 5, so the fourth fabrication methodis both simpler and more reliable than the third fabrication method.

[0110] The inter-layer dielectric films in the first through fourthfabrication methods can be etched by, for example, any of the followingmethods (1) to (4).

[0111] (1) Etching is performed for a fixed time set on the basis of thefilm thickness and etching rate.

[0112] (2) The inter-layer dielectric film has a dual structurecomprising an upper film formed of an etchable material such as siliconoxide or silicate glass, and a thin lower film formed of siliconnitride, which acts as an etch-stop layer. Etching is carried out untilthe upper film has been removed and the lower film is exposed. Anetching gas is then used to etch the lower film.

[0113] (3) The inter-layer dielectric film, which is formed of anetchable material such as silicon oxide or silicate glass, is depositedon an underlying dielectric film, such as a film of silicon nitride,that is not etched by the same etchant. Etching is stopped when thisunderlying dielectric film has been reached.

[0114] (4) The metal exposed by etching is detected, and a separate endpoint is set for each etching process on the basis of the detection ofthe metal.

[0115] The metal etching processes in the first and second fabricationmethods may performed by, for example, any of the following methods (a)to (c):

[0116] (a) Etching is performed for a fixed time set on the basis of themetal film thickness and etching rate.

[0117] (b) The metal is etched with an etching gas that does not etchthe barrier metal. When the barrier metal is exposed, the etchant ischanged to an etching gas that etches the barrier metal.

[0118] (c) A separate end point is set for each etching process bydetecting the inter-layer dielectric film exposed by the etchingprocess.

[0119] As described above, according to the first embodiment, arectangular metal bar 2 is aligned above the lower-layer conductive line1, in contact with or unitary with the lower-layer conductive line 1,and a rectangular metal bar 4 is aligned below the upper-layerconductive line 5, in contact with or unitary with the upper-layerconductive line 5. Rectangular metal bar 2 and rectangular metal bar 4make contact to establish an electrical connection between thelower-layer conductive line 1 and upper-layer conductive line 5. Thisarrangement can promote the achievement of smaller device geometries,because highly reliable interconnections can be formed in a stablemanner, even when the design rules specify very small feature sizes.

[0120] Second Embodiment

[0121]FIGS. 10A to 10C and 11A to 11C show the structure of asemiconductor device according to a second embodiment of the presentinvention. FIGS. 10A and 11A are partial plan views of the device, FIGS.10B and 11B are sectional views through line x-x′ in FIGS. 10A and 11A,respectively, and FIGS. 10C and 11C are sectional views through liney-y′ in FIGS. 10A and 11A, respectively. As shown in these drawings, thesemiconductor device includes a conductive line 31 in a lower conductivelayer, a first conductive member in the form of a rectangular metal bar32, an inter-layer dielectric film 33, a second conductive member in theform of a rectangular metal bar 34, and a conductive line 35 in an upperconductive layer. The rectangular metal bar 32 has a height h1, therectangular metal bar 34 has a height h2, and the lower-layer conductiveline 1 and upper-layer conductive line 5 are mutually separated by adistance d. In the interconnection structure in FIGS. 10A to 10C, thetwo conductive lines 31, 35 are straight and cross at substantially aright angle, being interconnected at the crossing point. In theinterconnection structure in FIGS. 11A to 11C, the lower-layerconductive line 31 bends at substantially a right angle and theupper-layer conductive line 35 terminates above the bend; thelower-layer conductive line 31 and the upper-layer conductive line 35are interconnected at the point of the bend. The interconnectionstructure in FIGS. 11A to 11C can also be modified as in FIGS. 3A to 3Cor FIGS. 4A to 4C in the first embodiment.

[0122] In the semiconductor device according to the second embodiment,rectangular metal bar 32 is aligned above the lower-layer conductiveline 31, and extends for part of the length of the lower-layerconductive line 31, while rectangular metal bar 34 is aligned below theupper-layer conductive line 35, and extends for part of the length ofthe upper-layer conductive line 35. Rectangular metal bar 32 is formedin contact with or is unitary with the lower-layer conductive line 31,while rectangular metal bar 34 is formed in contact with or is unitarywith the upper-layer conductive line 35. The rectangular metal bars 32,34 make mutual contact, thereby establishing an electrical path betweenlower-layer conductive line 31 and upper-layer conductive line 35. Aslot is formed in the surface of rectangular metal bar 32, andrectangular metal bar 34 makes contact with rectangular metal bar 32 byfitting into this slot.

[0123] In the second embodiment, since rectangular metal bar 34 fitsinto the slot in rectangular metal bar 32, the sum of the height hi ofrectangular metal bar 32 and the height h2 of rectangular metal bar 34is greater than the separation d between the lower-layer conductive line31 and upper-layer conductive line 35 (d<h1+h2). The separation d is,however, greater than either height h1 or h2 (d>h1 and d>h2). The widthsand the lengths of the rectangular metal bars 32, 34 are the same as thewidths and lengths of the rectangular metal bars 2, 4 in the firstembodiment, described above.

[0124] In a semiconductor device according to the second embodiment, asin the first embodiment, the height h1 of rectangular metal bar 32 andthe height h2 of rectangular metal bar 34 are both less than the depthof a through hole in a conventional semiconductor device with the samedesign rules. The aspect ratio of rectangular metal bar 32 (h1/surfacearea) and the aspect ratio of rectangular metal bar 34 (h2/surface area)are both less than the aspect ratio d/πr² of the conventional throughhole (refer to FIG. 14). For this reason, as in the first embodiment,the rectangular holes occupied by the rectangular metal bars 32, 34 canbe formed with greater stability than can the corresponding through holein a conventional semiconductor device. Furthermore, the rectangularmetal bars 32, 34 can be formed by photolithography and etching of metallayers, and the alignment tolerances in the photolithographic processcan be greater than in a conventional semiconductor device. In addition,the current density at the interface between the rectangular metal bars32, 34 is less than the conventional current density. Thus, theinterconnections in the multilayer wiring structure can be formed withgreater stability than in a conventional semiconductor device, and thereliability of the interconnections can be improved.

[0125] Since rectangular metal bar 34 sits in the slot formed in thesurface of rectangular metal bar 32, not only does the sum of the heighth1 of rectangular metal bar 32 and the height h2 of rectangular metalbar 34 exceed the separation d between the lower-layer conductive line31 and upper-layer conductive line 35, but the area of contact betweenthe rectangular metal bars 32, 34 exceeds the area of contact in thefirst embodiment. For this reason, the current density at the interfacebetween the rectangular metal bars 32, 34 can be reduced, as comparedwith the first embodiment, and the interconnection can be made morereliable.

[0126] A semiconductor device according to the second embodiment can befabricated by any of the four fabrication methods described in the firstembodiment, with the following modification. When the second rectangularhole is formed by etching, etching is not stopped when the surface ofrectangular metal bar 32 is exposed, but is continued to form the slotin rectangular metal bar 32 for receiving rectangular metal bar 34.Specifically, after rectangular metal bar 32 has been formed and theinter-layer dielectric film 33 is formed over the lower-layer conductiveline 31 and rectangular metal bar 32, a hole is etched in theinter-layer dielectric film 33 above rectangular metal bar 32, extendingto rectangular metal bar 32, using a fluorocarbon gas as an etching gas.This hole exposes the surface of rectangular metal bar 32. Next, theetching gas is changed to a chlorine or fluorine gas to remove part ofthe exposed rectangular metal bar 32, thereby forming the slot. Ifrectangular metal bar 32 is made of aluminum, chlorine gas is preferablyemployed as this etching gas. If rectangular metal bar 32 is made oftungsten, fluorine gas is preferably employed. Since these etching gasesmay also etch the photoresist forming the etching mask employed forformation of the hole exposing rectangular metal bar 32, the filmthickness of this photoresist mask is preferably thicker than in thefirst embodiment. The upper rectangular hole and the slot in the secondembodiment can be formed in a single chamber, without the need for anadditional photolithographic process for the slot.

[0127] If the third or fourth fabrication method of the first embodimentis employed, the metal material used for forming conductive lines by thedamascene process should be a material that can be etched.

[0128] According to the second embodiment as described above,rectangular metal bar 32, which is aligned in contact with or unitarywith the lower-layer conductive line 31, makes contact with rectangularmetal bar 34, which is aligned in contact with or unitary withrectangular metal bar 34, thereby establishing an electrical pathbetween the lower-layer conductive line 31 and the upper-layerconductive line 35. Stable, highly reliable formation ofinterconnections can be achieved even under fine-dimension design rules,enabling device geometries to be reduced, as in the first embodiment.Furthermore, the sum of the height h1 of rectangular metal bar 32 andthe height h2 of rectangular metal bar 34 exceeds the separation dbetween the lower-layer conductive line 31 and the upper-layerconductive line 35, and the current density at the interface between thefirst and second conductive members is lower than in the firstembodiment, so the reliability of the interconnections can be furtherimproved.

[0129] Third Embodiment

[0130]FIGS. 12A to 12 c show the structure of a semiconductor deviceaccording to a third embodiment of the invention. FIG. 12A is a partialplan view, FIG. 12B is a sectional view through line x-x′ in FIG. 12A,and FIG. 12C is a sectional view through line y-y′ in FIG. 12A. As shownin these drawings, the semiconductor device includes a conductive line41 in a lower conductive layer, a conductive member in the form of arectangular metal bar 42, an inter-layer dielectric film 43, a throughhole 44, and a conductive line 45 in an upper conductive layer.Rectangular metal.bar 42 has a height H1; the through hole 44 has adepth D2 and diameter r2. A separation d is provided between thelower-layer conductive line 41 and the upper-layer conductive line 45.In FIGS. 12A to 12 c, the lower-layer conductive line 41 bends atsubstantially at a right angle and the upper-layer conductive line 45terminates above the bend in the lower-layer conductive line 41; the endof the upper-layer conductive line 45 is interconnected to thelower-layer conductive line 51 at the point of the bend. The thirdembodiment is not limited to this structure, however; it is applicableto any of the multilayer wiring structures shown in the first embodiment(FIG. 1A through FIG. 4C).

[0131] In a semiconductor device according to the third embodiment, thefirst conductive member is the rectangular metal bar 42 that is alignedwith part of the lower-layer conductive line 41, and is either formed incontact with or is unitary with the lower-layer conductive line 41. Thethrough hole 44 is formed below one part of the upper-layer conductiveline 45, and is filled by a metal plug that either makes contact with oris unitary with the upper-layer conductive line 45, forming the secondconductive member. Rectangular metal bar 42 makes contact with the metalplug in the through hole 44, thereby establishing an electrical pathbetween the lower-layer conductive line 41 and the upper-layerconductive line 45.

[0132] The third embodiment is obtained from the first embodiment byreducing rectangular metal bar 4 to a metal plug disposed in the throughhole 44. In the third embodiment, the sum of the height H1 ofrectangular metal bar 42 and the depth D2 of the through hole 44 isequal to the separation d between the lower-layer conductive line 41 andthe upper-layer conductive line 45 (d=H1+D2). Accordingly, d>H1, andd>D2. The width and length of rectangular metal bar 42 are the same asthose of rectangular metal bar 2 in the first embodiment. The diameter 2r of the through hole 44 is the same as the diameter of the through hole63 in the conventional semiconductor device in FIG. 14.

[0133] Since the aspect ratio D2/πr² of the through hole 44 in the thirdembodiment is less than the aspect ratio d/πr² of a conventional throughhole 63 with the same design rules, the process that forms the throughhole 44 is more stable than the process that forms the conventionalthrough hole 63. Thus the use of a rectangular metal bar 42 and throughhole 44 to interconnect conductive lines in different layers leads tomore stable formation of interconnections than in the prior art, and thereliability of the interconnections is improved.

[0134] Since no second rectangular metal bar is formed in the thirdembodiment, even if two unrelated interconnections are laid out close toone another, the length of rectangular metal bar 42 is unconstrained.The length of rectangular metal bar 42 can therefore be set freely,regardless of the separation between adjacent conductive lines in theupper and lower conductive layers, and regardless of the wiring layoutof the device. The length of rectangular metal bar 42 can be optimizedaccording to such factors as parasitic capacitance between the upper andlower conductive layers, photolithographic alignment tolerances, and thedesign rules for the multilayer wiring structure.

[0135] A semiconductor device according to the third embodiment can befabricated by any of the four fabrication methods described in the firstembodiment, the through hole 44 being formed by the step that formed thesecond rectangular hole in the first embodiment, and filled with metalby the step that filled the second rectangular hole with metal in thefirst embodiment.

[0136] As described above, according to the third embodiment, arectangular metal bar 42 aligned in contact with or unitary with alower-layer conductive line 41 makes contact with a metal plug in athrough hole 44 aligned in contact with or unitary with an upper-layerconductive line 45, electrically interconnecting the lower-layerconductive line 41 and the upper-layer conductive line 45. Highlyreliable interconnections can be formed in this way even underfine-dimension design rules, enabling device geometries to be reduced,as in the first embodiment. Furthermore, since no second rectangularmetal bar is formed, the length of rectangular metal bar 42 is notconstrained by the separation between adjacent conductive lines in theupper and lower conductive layers and the layout of the device.

[0137] Fourth Embodiment

[0138]FIGS. 13A to 13C show the structure of a semiconductor deviceaccording to a fourth embodiment of the invention. FIG. 13A is a partialplan view, FIG. 13B is a sectional view through line x-x′ in FIG. 13A,and FIG. 13C is a sectional view through line y-y′ in FIG. 13A. As shownin these drawings, the semiconductor device includes a conductive line51 in a lower conductive layer, a through hole 52, an inter-layerdielectric film 53, a rectangular metal bar 54, and a conductive line 55in an upper conductive layer. The through hole 52 has a depth D1 anddiameter 2 r; the rectangular metal bar 54 has a height H2. A separationd is provided between the lower-layer conductive line 51 and theupper-layer conductive line 55. In FIG. 13A to FIG. 13C, the lower-layerconductive line 51 bends at substantially a right angle, and theupper-layer conductive line 55 terminates above the bend in thelower-layer conductive line 51; the end of the upper-layer conductiveline 55 is interconnected to the lower-layer conductive line 51 at thepoint of the bend. The fourth embodiment is not limited to thisstructure, however; it is applicable to any of the multilayer wiringstructures shown in the first embodiment (FIGS. 1A through 4C).

[0139] In a semiconductor device according to the fourth embodiment, thethrough hole 52 is aligned on one part of the lower-layer conductiveline 51. A first conductive member is formed by metal filling thethrough hole 52. The rectangular metal bar 54, which forms the secondconductive member, is aligned below the upper-layer conductive line 55,and extends for part of the length of the upper-layer conductive line55. The rectangular metal bar 54 is formed in contact with or is unitarywith the upper-layer conductive line 55. The metal plug in the throughhole 52 makes contact with rectangular metal bar 54, therebyestablishing an electrical path between the lower-layer conductive line51 and the upper-layer conductive line 55.

[0140] The fourth embodiment is obtained from the first embodiment byreducing rectangular metal bar 2 to a metal plug disposed in the throughhole 52. In the fourth embodiment, the sum of the depth D1 of thethrough hole 52 and the height H2 of rectangular metal bar 54 is equalto the separation d between the lower-layer conductive line 51 andupper-layer conductive line 55 (d=D1+H2). Accordingly, d>D1, and d>H2.The width and length of rectangular metal bar 54 are the same as thoseof rectangular metal bar 4 in the first embodiment. The diameter 2 r ofthe through hole 52 is the same as the diameter of the through hole 63in FIG. 14.

[0141] Since the aspect ratio D1πr/² of the through hole 52 in thefourth embodiment is less than the aspect ratio d/πr² of a conventionalthrough hole 63 with the same design rules, the process that forms thethrough hole 52 is more stable than the process that forms theconventional through hole 63. Thus the use of a rectangular metal bar 54and through hole 52 to interconnect conductive lines in different layersleads to more stable formation of interconnections than in the priorart, and the reliability of the interconnections is improved.

[0142] In a semiconductor device according to the fourth embodiment, therectangular metal bar 54 can be made longer than the through-holediameter 2 r. In the photolithographic process for forming therectangular metal bar 54, the alignment tolerance in the lengthwisedirection of the rectangular metal bar 54 with respect to the throughhole 52 can be less stringent than in a conventional semiconductordevice. This also leads to more stable formation of interconnections,and improves the reliability of the interconnections.

[0143] Since no first rectangular metal bar is formed in the fourthembodiment, even if two unrelated interconnections are laid out close toone another, the length of rectangular metal bar 54 is unconstrained.The length of rectangular metal bar 54 can therefore be set freely,regardless of the separation between adjacent conductive lines in theupper and lower conductive layers, and regardless of the wiring layoutof the device. The length of rectangular metal bar 54 can be optimizedaccording to such factors as parasitic capacitance between the upper andlower conductive layers, photolithographic alignment tolerances, and thedesign rules for the multilayer wiring structure.

[0144] A semiconductor device according to the fourth embodiment can befabricated by any of the four fabrication methods described in the firstembodiment. In the first, third, and fourth fabrication methods, thethrough hole 52 is formed by the etching step that formed the firstrectangular hole in the first embodiment, and is filled with metal bythe step that filled the first rectangular hole with metal in the firstembodiment. In the second fabrication method, the metal plug filling thethrough hole 52 is formed by the step that formed the first rectangularmetal bar in the first embodiment.

[0145] As described above, according to the fourth embodiment, a metalplug in a through hole 52 aligned in contact with or unitary with alower-layer conductive line 51 makes contact with a rectangular metalbar 54 aligned in contact with or unitary with an upper-layer conductiveline 55, electrically interconnecting the lower-layer conductive line 51and the upper-layer conductive line 55. Highly reliable interconnectionscan be formed in this way even under fine-dimension design rules,enabling device geometries to be reduced, as in the first embodiment.Furthermore, since no first rectangular metal bar is formed, the lengthof rectangular metal bar 54 is not constrained by the separation betweenadjacent conductive lines in the upper and lower conductive layers andthe layout of the device.

[0146] Although rectangular metal bars aligned above the lowerconductive layer and below the upper conductive layer were used asexamples of conductive members in the first thorough fourth embodiments,the conductive members are not limited to rectangular shapes. Othershapes, such as the shape of an ellipse or a rhombus, may be employed.The conductive members in the present invention may have any shape thatcan be formed on the inter-layer dielectric film within limits definedby conductive lines adjacent to the upper-layer or lower-layerconductive line to which the conductive member is connected, so that theconductive members do connect with the adjacent conductive lines. Thusthe width of a conductive member does not need to be the same, or evensubstantially the same, as the width of the conductive line to which theconductive layer is connected in the upper or lower conductive layer,provided that the conductive member does not become connected to anotheradjacent conductive line. In many cases, it suffices for the width ofthe conductive members above the lower conductive layer, for example, tobe less than the distance between the adjacent conductive lines in thelower conductive layer, and for the length of the conductive member tobe less than the distance between the two conductive lines in the upperconductive layer that are adjacent to the upper-layer conductive lineconnected to the lower-layer conductive line to which the conductivemember is connected.

[0147] As described above, the present invention enables the stableformation of highly reliable interconnections between differentconductive layers under smaller-dimension design rules thanconventionally, thereby contributing to the reduction of semiconductordevice geometries.

[0148] The fabrication methods described above fall into two generaltypes, which can be summarized as follows.

[0149] In one general type of fabrication method, a lower conductivelayer including a first conductive line is formed; a first dielectricfilm is deposited on the first conductive layer; a first hole is formedin the first dielectric film; the first hole is filled with a firstconductive material to form a first conductive member making contactwith the first conductive line; a second dielectric film is deposited onthe first dielectric film and the first conductive member; a second holeis formed in the second dielectric film; and an upper conductive layerand a second conductive member are formed, the upper conductive layerbeing disposed on the second dielectric film and including a secondconductive line, the second conductive member filling the second holeand making contact with the first conductive member and the secondconductive line. The first hole and the second hole extend for mutuallydifferent distances in at least one direction parallel to the upperconductive layer and the lower conductive layer.

[0150] In this method, the lower conductive layer may be formed bydepositing a lower dielectric film, forming a trench in the lowerdielectric film, and filling the trench with a second conductivematerial such as copper, thereby forming the first conductive line.

[0151] The second hole may be formed by etching the second dielectricfilm with an etching mask to expose the first conductive member, andetching the first dielectric film and the first conductive member withthe same etching mask, thereby forming a slot in the first conductivemember.

[0152] The upper conductive layer and second conductive member may beformed by depositing a first conductive film on the second dielectricfilm, thereby filling the second hole, then removing the firstconductive film from the second dielectric film, leaving the second holefilled to form the second conductive member; depositing a secondconductive film on the second dielectric film and the second conductivemember; and patterning the second conductive film to form the upperconductive layer.

[0153] Alternatively, the upper conductive layer and the secondconductive member may be formed by depositing a first conductive film onthe second dielectric film, the first conductive film filling the secondhole; removing the first conductive film from the second dielectricfilm, leaving the second hole filled to form the second conductivemember; depositing a third dielectric film on the second dielectric filmand the second conductive member; forming a trench in the thirddielectric film; and filling the trench with a second conductivematerial to form the second conductive line.

[0154] Another way of forming the upper conductive layer and the secondconductive member is to deposit a conductive film on the seconddielectric film, thereby filling the second hole, then pattern theconductive film to form the upper conductive layer.

[0155] Yet another way to form the upper conductive layer and the secondconductive member is to form a trench in the second dielectric film,such that the second hole extends from the trench to the firstconductive member, and fill the trench and the second hole with a secondconductive material to form the second conductive member and the secondconductive line.

[0156] In another general type of fabrication method, a lower conductivepattern having a first height is formed, the lower conductive patternincluding a first conductive line pattern; part of the first conductiveline pattern is masked by depositing a photoresist coating andpatterning the photoresist coating by photolithography; the lowerconductive pattern is etched to reduce the first height to a secondheight lower than the first height, thereby forming a lower conductivelayer in which all of the first conductive line pattern disposed belowthe second height constitutes a first conductive line, the masked partof the first conductive line pattern disposed above the second heightconstituting a first conductive member unitary with the first conductiveline; a dielectric film is deposited on the lower conductive layer andthe first conductive member; a hole is formed in the dielectric film,the hole extending to the first conductive member; and an upperconductive layer and a second conductive member are formed, the upperconductive layer being disposed on the dielectric film and including asecond conductive line, the second conductive member filling the hole inthe dielectric film and making contact with the first conductive memberand the second conductive line. The first conductive member and the holein the dielectric film extend for mutually different distances in atleast one direction parallel to the upper conductive layer and the lowerconductive layer.

[0157] In this second general method, the upper conductive layer and thesecond conductive member may be formed by depositing a conductive filmon the dielectric film, the conductive film filling the hole, thenpatterning the conductive film to form the upper conductive layer.

[0158] Alternatively, the upper conductive layer and the secondconductive member may be formed by forming a trench in the dielectricfilm, such that the hole extends from the trench to the first conductivemember, and filling the trench and the hole with a second conductivematerial to form the second conductive member and the second conductiveline.

[0159] The hole may be formed by etching the dielectric film with anetching mask to expose the first conductive member, and continuing toetch the dielectric film and the first conductive member with the sameetching mask, thereby forming a slot in the first conductive member.

[0160] A few variations of the preceding embodiments have been mentionedabove, but those skilled in the art will recognize that furthervariations are possible within the scope of the appended claims.

What is claimed is:
 1. A semiconductor device having a first conductivelayer including a first conductive pattern and a second conductive layerincluding a second conductive pattern, the first conductive layer beingseparated from the second conductive layer by an inter-layer distance,the semiconductor device comprising: a first conductive member disposedbetween the lower conductive layer and the second conductive layer,having a first height less than the inter-layer distance, making contactwith the first conductive pattern; and a second conductive memberdisposed between the lower conductive layer and the second conductivelayer, having a second height less than the inter-layer distance, makingcontact with the first conductive member and the second conductivepattern; wherein the first conductive member and the second conductivemember extend for mutually different distances in at least one directionparallel to the first conductive layer and the second conductive layer.2. The semiconductor device of claim 1, wherein the first conductivemember and the second conductive member both comprise a metal material.3. The semiconductor device of claim 1, wherein the first conductivemember is unitary with the first conductive pattern.
 4. Thesemiconductor device of claim 1, wherein the first conductive member hasa width and a length both equal to a width of the second conductivepattern.
 5. The semiconductor device of claim 1, wherein: the firstconductive pattern extends in a first direction; the second conductivepattern extends in a second direction different from the firstdirection; the first conductive pattern is disposed between a first pairof conductive patterns in the first conductive layer, the first pair ofconductive patterns being mutually separated by a first distance in thesecond direction; the second conductive pattern is disposed between asecond pair of conductive patterns in the second conductive layer, thesecond pair of conductive patterns being mutually separated by a seconddistance in the first direction; the first conductive member extends inthe first direction for less than the second distance, and extends inthe second direction for less than the first distance; and the secondconductive member extends in the first direction for less than thesecond distance, and extends in the second direction for less than thefirst distance.
 6. The semiconductor device of claim 1, wherein: thefirst conductive member has a width equal to a width of the firstconductive pattern and extends parallel to the first conductive patternfor a first length exceeding a width of the second conductive pattern;and the second conductive member has a width equal to the width of thesecond conductive pattern, and extends parallel to the second conductivepattern for a length exceeding the width of the first conductivepattern.
 7. The semiconductor device of claim 6, wherein the length ofthe first conductive member exceeds the length of the second conductivemember.
 8. The semiconductor device of claim 6, wherein the firstconductive member and the second conductive member extend in differentlengthwise directions, and the first conductive member has a slotaccommodating the second conductive member.
 9. A semiconductor devicecomprising: an insulating film having a first surface and a secondsurface, the first surface and the second surface being mutuallyopposite; a plurality of first conductive lines, formed on said firstsurface, spaced apart from each other in a first direction; a pluralityof second conductive lines, formed on said second surface, spaced apartfrom each other in a second direction different from the firstdirection, one of the second conductive lines being electricallyconnected to one of the first conductive lines; a first conductor formedon said one of the first conductive lines, the first conductor having afirst width shorter than a distance in the first direction between saidone of the first conductive lines and another one of the firstconductive lines adjoining said one of the first conductive lines, thefirst conductor having a second width shorter than a distance in thesecond direction between said one of the second conductive lines andanother one of the second conductive lines adjoining said one of thesecond conductive lines; and a second conductor formed under said one ofthe second conductive lines, the second conductor having a third widthshorter than a distance in the first direction between said one of thefirst conductive lines and said another one of the first conductivelines adjoining said one of the first conductive lines, the secondconductor having a fourth width shorter than a distance in the seconddirection between said one of the second conductive lines and saidanother one of the second conductive lines adjoining said one of thesecond conductive lines; wherein the first conductive line iselectrically connected to the second conductive line by contact of saidfirst conductor with said second conductor in said insulating film. 10.The semiconductor device of claim 9, wherein the sum of a height of saidfirst conductor and a height of said second conductor is substantiallyequal to a distance between an upper surface of said one of the firstconductive lines and a lower surface of said one of the secondconductive lines.
 11. The semiconductor device of claim 9, wherein oneof said first conductor and said second conductor has a slot, and saidfirst conductor and said second conductor are electrically connected byinterlocking at said slot.
 12. The semiconductor device of claim 9,wherein the first width of said first conductor is substantially equalto a width of said one of the first conductive lines, said firstconductor is longer in a direction extending along said one of the firstconductive line than the first width of said first conductor, the fourthwidth of said second conductor is substantially equal to a width of saidone of the second conductive lines, and said second conductor is longerin a direction extending along said one of the second conductive linesthan the fourth width of said second conductor.
 13. The semiconductordevice of claim 9, wherein one of said first conductor and said secondconductor is smaller than another one of said first conductor and saidsecond conductor.
 14. The semiconductor device of claim 9, wherein saidone of the first conductive lines and said first conductor are formedfrom a single conductive layer.
 15. The semiconductor device of claim 9,wherein said first conductive lines, said second conductive lines, saidfirst conductor, and said second conductor are formed from a metalmaterial.
 16. The semiconductor device of claim 15, wherein said metalmaterial comprises aluminum.
 17. The semiconductor device of claim 15,wherein said metal material comprises copper.